The present invention generally relates to remote control systems of the type used to control TV receivers, disc players and video cassette recorders (VCRs), and more particularly to a technique for significantly increasing the battery life in the transmitters of such remote control systems.
Wireless remote control of television receivers, disc players and VCRs typically involves the transmission of an infrared or ultrasonic signal from a battery-powered transmitter. Infrared control systems are less susceptible to interference signals than are ultrasonic control systems, but there is some concern that the human eye may be harmed when subjected to continuous direct exposure to infrared radiation. In either type of system, certain continuous functions, such as volume or brightness, must be controlled. In practice, the selected function is increased or decreased as long as the user continues to depress the appropriate key on the transmitter. In some prior art systems, a signal is transmitted for as long as the key remains depressed. This not only increases the potential harm to the human eye that may be inadvertently subjected to continuous direct exposure from an infrared transmitter, but in both the infrared and ultrasonic systems, battery life is significantly decreased.
A typical example of an infrared remote control transmitter employs the NEC .mu.PD1913C integrated circuit (IC). FIG. 1 illustrates the manner in which this transmitter IC operates the infrared (IR) light emitting diode (LED) to control continuous functions. A command identifying the nature of the continuous function and the direction of change is conveyed on the initial 67.5 msec. of transmission. The command is followed by a pair of pulses (one 9 msec. pulse and one 0.56 msec. pulse) occurring every 108 msec. for as long as the continuous function key remains depressed. The remote receiver changes the continuous function until it no longer receives these pulses. Thus, as shown in FIG. 1, the portion of the signal that conveys command information (the first 67.5 msec. of transmission) consists of a 9 msec. leader pulse followed by thirty-three 0.56 msec. pulses. Each 9 msec. and 0.56 msec. pulse consists of a series of shorter-duration pulses occurring at a rate defined by the carrier signal. The carrier signal turns the LED on 8.77 .mu.sec. in each 26.3 .mu.sec. which is a 33% duty cycle.
The total time the LED is on when a single 67.5 msec. command is transmitted is ##EQU1##
Assuming a continuous function key is depressed for T seconds, the total on time for the LED is ##EQU2##
Although transmitter ICs available from other manufacturers use different modulation schemes, carrier frequencies and data formats, all known remote transmitters continue to transmit a signal in some fashion to accomplish the control of continuous functions. As a result, extensive use of continuous functions can significantly shorten battery life.